Sequential method for depositing a film by modulated ion-induced atomic layer deposition (MII-ALD)

ABSTRACT

The present invention relates to an enhanced sequential atomic layer deposition (ALD) technique suitable for deposition of barrier layers, adhesion layers, seed layers, low dielectric constant (low-k) films, high dielectric constant (high-k) films, and other conductive, semi-conductive, and non-conductive films. This is accomplished by 1) providing a non-thermal or non-pyrolytic means of triggering the deposition reaction; 2) providing a means of depositing a purer film of higher density at lower temperatures; and, 3) providing a faster and more efficient means of modulating the deposition sequence and hence the overall process rate resulting in an improved deposition method.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. Utility applicationSer. No. 09/812,285, filed Mar. 19, 2001 and claims benefit of U.S.Utility application Ser. No. 09/812,285, U.S. Utility application Ser.No. 09/812,486, and U.S. Utility application Ser. No. 09/812,352; allfiled Mar. 19, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to the field of advancedthin film deposition methods commonly used in the semiconductor, datastorage, flat panel display, as well as allied or other industries. Moreparticularly, the present invention relates to an enhanced sequential ornon-sequential atomic layer deposition (ALD) apparatus and techniquesuitable for deposition of barrier layers, adhesion layers, seed layers,low dielectric constant (low-k) films, high dielectric constant (high-k)films, and other conductive, semi-conductive, and non-conductive thinfilms.

[0004] The disadvantages of conventional ALD are additionally discussedin a copending application with the same assignee entitled “Method andApparatus for Improved Temperature Control in Atomic Layer Deposition”,which is hereby incorporated by reference in its entirety and may befound as copending application Ser. No. 09/854,092.

[0005] 2. Brief Description of the Background Art

[0006] As integrated circuit (IC) dimensions shrink and the aspectratios of the resulting features increase, the ability to depositconformal, ultra-thin films on the sides and bottoms of high aspectratio trenches and vias becomes increasingly important. These conformal,ultra-thin films are typically used as “liner” material to enhanceadhesion, prevent inter-diffusion and/or chemical reaction between theunderlying dielectric and the overlying metal, and promote thedeposition of a subsequent film.

[0007] In addition, decreasing device dimensions and increasing devicedensities has necessitated the transition from traditional CVD tungstenplug and aluminum interconnect technology to copper interconnecttechnology. This transition is driven by both the increasing impact ofthe RC interconnect delay on device speed and by the electromigration(i.e., the mass transport of metal due to momentum transfer betweenconducting electrons and diffusing metal atoms, thereby affectingreliability) limitations of aluminum based conductors for sub 0.25 μmdevice generations. Copper is preferred due to its lower resistivity andhigher (greater than 10 times) electromigration resistance as comparedto aluminum. A single or dual damascene copper metallization scheme isused since it eliminates the need for copper etching and reduces thenumber of integration steps required. However, the burden now shifts tothe metal deposition step(s) as the copper must fill predefined highaspect ratio trenches and/or vias in the dielectric. Electroplating hasemerged as the copper fill technique of choice due to its low depositiontemperature, high deposition rate, and potential low manufacturing cost.

[0008] Two major challenges exist for copper wiring technology: thebarrier and seed layers. Copper can diffuse readily into silicon andmost dielectrics. This diffusion may lead to electrical leakage betweenmetal wires and poor device performance. An encapsulating barrier layeris needed to isolate the copper from the surrounding material (e.g.,dielectric or Si), thus preventing copper diffusion into and/or reactionwith the underlying material (e.g. dielectric or Si). In addition, thebarrier layer also serves as the adhesion or glue layer between thepatterned dielectric trench or via and the copper used to fill it. Thedielectric material can be a low dielectric constant, i.e. low-kmaterial (used to reduce inter- and intra-line capacitance andcross-talk) which typically suffers from poorer adhesion characteristicsand lower thermal stability than traditional oxide insulators.Consequently, this places more stringent requirements on the barriermaterial and deposition method. An inferior adhesion layer will, forexample, lead to delamination at either the barrier-to-dielectric orbarrier-to-copper interfaces during any subsequent anneal and/orchemical mechanical planarization (CMP) processing steps leading todegradation in device performance and reliability. Ideally, the barrierlayer should be thin, conformal, defect free, and of low resistivity soas to not compromise the conductance of the copper metal interconnectstructure.

[0009] In addition, electroplating fill requires a copper seed layer,which serves to both carry the plating current and act as the nucleationlayer. The preferred seed layer should be smooth, continuous, of highpurity, and have good step coverage with low overhang. A discontinuityin the seed layer will lead to sidewall voiding, while gross overhangwill lead to pinch-off and the formation of top voids.

[0010] Both the barrier and seed layers which are critical to successfulimplementation of copper interconnects require a means of depositinghigh purity, conformal, ultra-thin films at low substrate temperatures.

[0011] Physical vapor deposition (PVD) or sputtering has been adopted asthe preferred method of choice for depositing conductor films used in ICmanufacturing. This choice has been primarily driven by the low cost,simple sputtering approach whereby relatively pure elemental or compoundmaterials can be deposited at relatively low substrate temperatures. Forexample, refractory based metals and metal compounds such as tantalum(Ta), tantalum nitride (TaN_(x)), other tantalum containing compounds,tungsten (W), tungsten nitride (WN_(x)), and other tungsten containingcompounds which are used as barrier/adhesion layers can be sputterdeposited with the substrate at or near room temperature. However, asdevice geometries have decreased, the step coverage limitations of PVDhave increasingly become an issue since it is inherently a line-of-sightprocess. This limits the total number of atoms or molecules which can bedelivered into the patterned trench or via. As a result, PVD is unableto deposit thin continuous films of adequate thickness to coat the sidesand bottoms of high aspect ratio trenches and vias. Moreover,medium/high-density plasma and ionized PVD sources developed to addressthe more aggressive device structures are still not adequate and are nowof such complexity that cost and reliability have become seriousconcerns.

[0012] Chemical vapor deposition (CVD) processes offer improved stepcoverage since CVD processes can be tailored to provide conformal films.Conformality ensures the deposited films match the shape of theunderlying substrate, and the film thickness inside the feature isuniform and equivalent to the thickness outside the feature.Unfortunately, CVD requires comparatively high deposition temperatures,suffers from high impurity concentrations, which impact film integrity,and have higher cost-of-ownership due to long nucleation times and poorprecursor gas utilization efficiency. Following the tantalum containingbarrier example, CVD Ta and TaN films require substrate temperaturesranging from 500° C. to over 800° C. and suffer from impurityconcentrations (typically of carbon and oxygen) ranging from several totens of atomic % concentration. This generally leads to high filmresistivities (up to several orders of magnitude higher than PVD), andother degradation in film performance. These deposition temperatures andimpurity concentrations make CVD Ta and TaN unusable for ICmanufacturing, in particular for copper metallization and low-kintegration.

[0013] Chen et al. (“Low temperature plasma-assisted chemical vapordeposition of tantalum nitride from tantalum pentabromide for coppermetallization”, J. Vac. Sci. Technol. B 17(1), pp. 182-185 (1999); and“Low temperature plasma-promoted chemical vapor deposition of tantalumfrom tantalum pentabromide for copper metallization”, J. Vac. Sci.Technol. B 16(5), pp. 2887-2890 (1998)) have demonstrated aplasma-assisted (PACVD) or plasma-enhanced (PECVD) CVD approach usingtantalum pentabromide (TaBr₅) as the precursor gas to reduce thedeposition temperature. Ta and TaN_(x) films were deposited from 350° C.to 450° C. and contained 2.5 to 3 atomic % concentration of bromine.Although the deposition temperature has been reduced by increasedfragmentation (and hence increased reactivity) of the precursor gases inthe gas-phase via a plasma, the same fragmentation leads to thedeposition of unwanted impurities. Gas-phase fragmentation of theprecursor into both desired and undesired species inherently limits theefficacy of this approach.

[0014] Recently, atomic layer chemical vapor deposition (AL-CVD) oratomic layer deposition (ALD) has been proposed as an alternative methodto CVD for depositing conformal, ultra-thin films at comparatively lowertemperatures. ALD is similar to CVD except that the substrate issequentially exposed to one reactant at a time. Conceptually, it is asimple process: a first reactant is introduced onto a heated substratewhereby it forms a monolayer on the surface of the substrate. Excessreactant is pumped out. Next a second reactant is introduced and reactswith the first reactant to form a monolayer of the desired film via aself-limiting surface reaction. The process is self-limiting since thedeposition reaction halts once the initially adsorbed (physi- orchemi-sorbed) monolayer of the first reactant has fully reacted with thesecond reactant. Finally, the excess second reactant is evacuated. Theabove sequence of events comprises one deposition cycle. The desiredfilm thickness is obtained by repeating the deposition cycle therequired number of times.

[0015] In practice, ALD is complicated by the painstaking selection of aprocess temperature setpoint wherein both: 1) at least one of thereactants sufficiently adsorbs to a monolayer and 2) the surfacedeposition reaction can occur with adequate growth rate and film purity.If the substrate temperature needed for the deposition reaction is toohigh, desorption or decomposition of the first adsorbed reactant occurs,thereby eliminating the layer-by-layer process. If the temperature istoo low, the deposition reaction may be incomplete (i.e., very slow),not occur at all, or lead to poor film quality (e.g., high resistivityand/or high impurity content). Since the ALD process is entirelythermal, selection of available precursors (i.e., reactants) that fitthe temperature window becomes difficult and sometimes unattainable. Dueto the above-mentioned temperature related problems, ALD has beentypically limited to the deposition of semiconductors and insulators asopposed to metals. ALD of metals has been confined to the use of metalhalide precursors. However, halides (e.g., Cl, F, Br) are corrosive andcan create reliability issues in metal interconnects.

[0016] Continuing with the TaN example, ALD of TaN films is confined toa narrow temperature window of 400° C. to 500° C., generally occurs witha maximum deposition rate of 0.2 Å/cycle, and can contain up to severalatomic percent of impurities including chlorine and oxygen. Chlorine isa corrosive, can attack copper, and lead to reliability concerns. Theabove process is unsuitable for copper metallization and low-kintegration due to the high deposition temperature, slow depositionrate, and chlorine impurity incorporation.

[0017] In conventional ALD of metal films, gaseous hydrogen (H₂) orelemental zinc (Zn) is often cited as the second reactant. Thesereactants are chosen since they act as a reducing agent to bring themetal atom contained in the first reactant to the desired oxidationstate in order to deposit the end film. Gaseous, diatomic hydrogen (H₂)is an inefficient reducing agent due to its chemical stability, andelemental zinc has low volatility (e.g., it is very difficult to deliversufficient amounts of Zn vapor to the substrate) and is generallyincompatible with IC manufacturing. Unfortunately, due to thetemperature conflicts that plague the ALD method and lack of kineticallyfavorable second reactant, serious compromises in process performanceresult.

[0018] In order to address the limitations of traditional thermal orpyrolytic ALD, radical enhanced atomic layer deposition (REALD, U.S.Pat. No. 5,916,365) or plasma-enhanced atomic layer deposition has beenproposed whereby a downstream radio-frequency (RF) glow discharge isused to dissociate the second reactant to form more reactive radicalspecies which drives the reaction at lower substrate temperatures. Usingsuch a technique, Ta ALD films have been deposited at 0.16 to 0.5Å/cycle at 25° C., and up to approximately 1.67 Å/cycle at 250° C. to450° C. Although REALD results in a lower operating substratetemperature than all the aforementioned techniques, the process stillsuffers from several significant drawbacks. Higher temperatures muststill be used to generate appreciable deposition rates. Suchtemperatures are still too high for some films of significant interestin IC manufacturing such as polymer-based low-k dielectrics that arestable up to temperatures of only 200° C. or less. REALD remains athermal or pyrolytic process similar to ALD and even CVD since thesubstrate temperature provides the required activation energy for theprocess and is therefore the primary control means for driving thedeposition reaction.

[0019] In addition, Ta films deposited using REALD still containchlorine as well as oxygen impurities, and are of low density. A lowdensity or porous film leads to a poor barrier against copper diffusionsince copper atoms and ions have more pathways to traverse the barriermaterial. Moreover, a porous or under-dense film has lower chemicalstability and can react undesirably with overlying or underlying films,or with exposure to gases commonly used in IC manufacturing processes.

[0020] Another limitation of REALD is that the radical generation anddelivery is inefficient and undesirable. RF plasma generation ofradicals used as the second reactant such as atomic H is not asefficient as microwave plasma due to the enhanced efficiency ofmicrowave energy transfer to electrons used to sustain and dissociatereactants introduced in the plasma. Furthermore, having a downstreamconfiguration whereby the radical generating plasma is contained in aseparate vessel located remotely from the main chamber where thesubstrate is situated and using a small aperture to introduce theradicals from the remote plasma vessel to the main chamber bodysignificantly decreases the efficiency of transport of the secondradical reactant. Both gas-phase and wall recombination will reduce theflux of desired radicals that can reach the substrate. In the case ofatomic H, these recombination pathways will lead to the formation ofdiatomic H₂, a far less effective reducing agent. If the plasma used togenerate the radicals was placed directly over the substrate, then thedeposition of unwanted impurities and particles can occur similarly tothe case of plasma-assisted CVD.

[0021] Finally, ALD (or any derivative such as REALD) is fundamentallyslow since it relies on a sequential process whereby each depositioncycle is comprised of at least two separate reactant flow and evacuationsteps, which can occur on the order of minutes with conventional valveand chamber technology. Significant improvements resulting in faster ALDare needed to make it more suitable for commercial IC manufacturing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a schematic of a deposition system suitable formodulated ion-induced atomic layer deposition (MII-ALD).

[0023]FIG. 2A depicts a timing sequence for an improved ALD methodincorporating periodic exposure of the substrate to ions.

[0024]FIG. 2B is another timing sequence for an improved ALD methodincorporating periodic exposure of the substrate to ions.

[0025]FIG. 3A shows the MII-ALD method utilizing ion flux modulation tovary the substrate exposure to ions.

[0026]FIG. 3B shows the timing of the MII-ALD method utilizing ionenergy modulation to vary the substrate exposure to ions by varying thesubstrate bias.

[0027] FIGS. 4A-F show methods of modulating the MII-ALD process.

[0028]FIG. 5 shows an electrostatic chuck (ESC) system suitable formodulating the ion energy in the MII-ALD process: a) in topologicalform; and, b) as an equivalent electrical circuit.

SUMMARY AND DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention relates to methods and apparatuses useablefor the deposition of conformal solid thin films of one or more elementsat low temperature. More particularly, the present invention relates toan enhanced sequential or, more preferably, non-sequential atomic layerdeposition apparatus and technique suitable for deposition of barrierlayers, adhesion layers, seed layers, and low dielectric constant(low-k) films, high dielectric constant (high-k) films, and otherconductive, semi-conductive, and non-conductive thin films.

[0030] More specifically, the present invention resolves the previouslypresented problems encountered in the prior art (e.g., REALD) by 1)providing a non-thermal or non-pyrolytic means of triggering thedeposition reaction; 2) providing a means of depositing a purer film ofhigher density at lower temperatures; 3) providing a faster and moreefficient means of modulating the deposition sequence and hence theoverall process rate resulting in an improved deposition method; and, 4)providing a means of improved radical generation and delivery.

[0031] Improvements to ALD processing, e.g., the REALD mentionedpreviously, remain “thermal” or “pyrolytic” processes since thesubstrate temperature provides the required activation energy and is theprimary control knob for driving the deposition reaction. Alternatively,we propose a novel approach by providing the required activation energyfrom a “non-thermal” source. In particular, we propose driving thedeposition reaction primarily via substrate exposure to impinging ionswherein the ions are used to deliver the necessary activation energy tothe near surface atoms and adsorbed reactant(s) via collision cascades.

[0032] Conventional deposition processes used in the semiconductorindustry (including ALD) typically deposit materials at temperatures inthe range of 300-600° C. The deposition method described herein can beeffected at much lower temperatures, in practice as low as 25° C. orbelow. Note that this process is ion-triggered (i.e., ion-induced) asopposed to ion-assisted in that deposition will not generally occurwithout ion bombardment since ions are used as the primary means ofproviding the activation energy required for deposition. A primarybenefit of ion-induced processing is the deposition of higher densityfilms of superior purity and adhesion properties. This result occurs dueto ion bombardment induced densification.

[0033]FIG. 1 illustrates a deposition system suitable for modulatedion-induced atomic layer deposition (MII-ALD). The invention describedherein also incorporates a means of modulating the exposure of thesubstrate to ions. By modulating 1) the ion flux; 2) the energy of theions striking the substrate; or a combination of (1) and (2), thedeposition reaction can be precisely toggled “on” or “off”. If the ionflux or energy is at a “low” state, then no deposition results ordeposition occurs so slowly that essentially no deposition results. Ifthe impinging ion flux or energy is at a “high” state, then depositionoccurs. Since the substrate (which may be a “bare” substrate, e.g., asilicon wafer before any films have been deposited, or it may be asubstrate which may already have had one or more films deposited on itssurface) 181 is preferably maintained at a low substrate temperature,the first and second reactants do not thermally react with anyappreciable rate or do not react at all. Instead, the depositionreaction only takes place when either the ion flux or ion energy istoggled to a suitable “high state”. The desired film thickness is builtup by repeating the ion pulses (either of flux or energy) the requirednumber of cycles. Furthermore, since modulation of the ion flux or ionenergy can occur on a much faster time scale (KHz range) than theconventional valve and pump technology used in ALD (up to minutes percycle), this deposition method is more suitable for commercial ICmanufacturing. This method shall be referred to herein as modulatedion-induced atomic layer deposition (MII-ALD).

[0034] In addition, the present invention also improves upon the priorart by employing a microwave generated plasma 172 substantiallycontained in the main chamber body 190 that is isolated via adistribution showerhead 171 comprised of a series or array of apertures175 which resolves the issues of radical generation and delivery, whilepreventing gas-phase precursor cracking (i.e., fragmentation or breakingdown the precursor gas into its constituent elements) and impurityand/or particle generation directly above the wafer 181. The plasma iscontained within the plasma source chamber 170 itself and is not indirect communication with the substrate 181. In MII-ALD, the same plasmais used to generate both ions 177 (used to drive the surface reactions)and radicals 176 (used as the second reactant), but is isolated from thefirst reactant 100 which typically contains both the principalelement(s) desired in the end film, but also unwanted impuritycontaining byproducts. Therefore, primarily only the radicals 176 andions 177 are able to travel through the showerhead apertures 175. Theplasma 172 is essentially contained within the plasma source chamber anddoes not intermingle with the precursor gases 100, 120.

[0035] The present invention utilizes ion imparted kinetic energytransfer rather than thermal energy (e.g., REALD, ALD, PECVD, CVD, etc.)to drive the deposition reaction. Since temperature can be used as asecondary control variable, with this enhancement films can be depositedusing MII-ALD at arbitrarily low substrate temperatures (generally lessthan 350° C.). In particular, films can be deposited at or near roomtemperature (i.e., 25° C.) or below.

[0036] The system of FIG. 1 contains a substantially enclosed plasmasource chamber 170 located in substantial communication with or, morepreferably, substantially within a main chamber body 190. The plasma 172is used to dissociate feed gases 130, 110 to generate both ions 177 andradicals 176. Typical feed gases 130 used for ion generation include,but are not restricted to Ar, Kr, Ne, and Xe. Typical feed gases 110(e.g., precursor B) used for radical generation include, but are notrestricted to H₂, O₂, N₂, NH₃, and H₂O vapor. The ions 177 are used todeliver the energy needed to drive surface reactions between the firstadsorbed reactant and the generated radicals 176. Inductively coupled RF(e.g., 400 KHz, 2 MHz, 13.56 MHz, etc.) power 160 can be used togenerate the plasma via solenoidal coils located within or outside ofthe plasma chamber (not shown in FIG. 1). More preferably, microwave(e.g., generally 2.45 GHz or higher frequencies) power 160 is coupled tothe plasma source chamber 170 via a suitable means such as a waveguideor coaxial cable. Microwave energy can be more efficiently transferredto ionizing electrons, leading to higher ionization fractions. This isof particular importance in the generation of radicals 176 (i.e., achemical fragment of a larger molecule) such as atomic hydrogen, or anyof a number of other reactive groups such as nitrogen atoms (N), oxygenatoms (O), OH molecules, or NH molecules, or a combination thereof.These radicals serve as the second reactant. Microwave orradio-frequency (RF) power 160 is coupled to the plasma 172 via adielectric material 173, which may be a dielectric window such as quartzembedded in the chamber wall, or it may be empty space in the case of amicrowave or RF antenna located within the plasma chamber.

[0037] In addition, a distribution showerhead 171, containing a seriesor array of apertures 175 through which ions 177 and radicals 176 aredelivered to the substrate 181, isolates the main process chamber 180from the plasma source chamber 170. A pressure drop (for example, a 5 or10 times decrease in pressure, with the main processing chamber 180being at the lower pressure) is thereby created between the plasmasource chamber 170 and the main processing chamber 180 to project theions 177 and radicals 176 to the substrate 181 via the distributionshowerhead 171. The plasma source chamber 170 is generally of comparablediameter to the main chamber body 190 to enable large area exposure ofthe sample. The size, aspect ratio, and distribution of the showerheadapertures 175 can be optimized to provide uniform exposure of thesubstrate 181 and the desired ion 177 to radical 176 ratio. The distancebetween this showerhead 171 and the substrate 181 may vary depending onthe application. For the processing of wafers in the IC industry, thisdistance is preferably at most two wafer diameters and more preferablyless than or equal to one half a wafer diameter.

[0038] Having a substantially enclosed plasma generation chamber 170situated within the main chamber 190 allows efficient and uniformdelivery of ions 177 and radicals 176 to the substrate 181. In addition,by isolating the plasma 172 from the main chamber 180 prevents gas-phasecracking of the first reactant 100 (e.g., precursor A), which isintroduced directly to the main processing chamber 180 via a gasdistribution manifold 199. Precursor A 100 may be any one or more of aseries of gaseous compounds used for depositing semiconductors,insulators, metals or the like that are well-known in the art (e.g,PDEAT (pentakis(diethylamido)tantalum), PEMAT(pentakis(ethylmethylamido)tantalum), TaBr₅, TaCl₅, TBTDET (t-butyliminotris(diethylamino) tantalum), TiCl₄, TDMAT(tetrakis(dimethylamido)titanium), TDEAT(tetrakis(diethylamino)titanium), CuCl, Cupraselect®((Trimethylvinylsilyl)hexafluoroacetylacetonato Copper I), W(CO)₆, WF₆,etc.) and examples will be further discussed herein. Finally, theion/radical distribution showerhead 171 shields the dielectric wall 173adjacent to the supplied RF or microwave power 160 against being coatedby precursor A 100 during processing which can degrade power transfer tothe plasma 172 in processing systems found in the prior art. This is ofparticular importance in the case of deposition of conductors whereby ifthe dielectric 173 is fully exposed to the metal containing firstreactant 100 (e.g., precursor A) and if the plasma 172 was directlygenerated within the main chamber 190 without the use of an isolatingdistribution showerhead 171, then metal deposition onto the dielectric173 will eventually shield out RF or microwave power 160 from the plasma172 such that the plasma 172 will extinguish.

[0039]FIG. 2A depicts a sequence for an improved ALD methodincorporating periodic exposure of the substrate to ions. In thisvariant of the method, ion exposure 230 begins with the introduction ofthe second precursor 220 (especially when plasma generated radicals 176are used as the second precursor or reactant). This figure illustratesone embodiment of MII-ALD utilizing the apparatus described in FIG. 1.This results in an enhanced sequential ALD process as follows:

[0040] 1) First exposure 200: The substrate 181 is exposed to a firstgaseous reactant 100 (e.g., precursor A), allowing a monolayer of thereactant to form on the surface. The substrate 181 may be at anytemperature below the decomposition temperature of the first gaseousreactant although it is preferable for the temperature to generally beless than approximately 350° C.

[0041] 2) First evacuation 210: The excess reactant 100 is removed byevacuating 214 the chamber 180 with a vacuum pump 184.

[0042] 3) Second exposure 220: Unlike conventional ALD, the substrate181 is simultaneously exposed to ions 177 and a second gaseous reactant(e.g., microwave or RF plasma generated radicals 176) during this stepwith the substrate 181 (e.g., wafer) biased to a negative potentialV_(bias) 185. Microwave or RF power 160 is supplied into the plasmachamber 170 to generate both the ions 177 (e.g., argon-ion (Ar⁺)) andradicals 176 (e.g., H atoms). The ions will strike the wafer 181 with anenergy approximately equal to (e|V_(bias)|+e|V_(p)|) where V_(p) is theplasma 172 potential (typically 10V to 20V). V_(bias) (−20V to −500V) istypically chosen to be greater than V_(p) in magnitude, and is used tocontrol the ion 177 energy. With the activation energy now primarilysupplied by ions 177 instead of thermal energy, the first and second(chemi- or physi-sorbed) reactants react via an ion-induced surfacereaction to produce a solid thin monolayer of the desired film at areduced substrate temperature below conventional ALD. The depositionreaction between the first and second reactants is self-limiting in thatthe reaction between them terminates after the initial monolayer of thefirst reactant 100 is consumed.

[0043] 4) Second evacuation 210: The excess second reactant is removedby again evacuating 216 the chamber 180 with the vacuum pump 184.

[0044] 5) Repeat: The desired film thickness is built up by repeatingthe entire process cycle (steps 1-4) many times.

[0045] Additional precursor gases (e.g., 120, 140) may be introduced andevacuated as required for a given process to create tailored films ofvarying compositions or materials. As an example, an optional exposuremay occur in the case of a compound barrier of varying composition. Forexample, a TaN_(x)/Ta film stack is of interest in copper technologysince TaN_(x) prevents fluorine attack from the underlying fluorinatedlow-k dielectrics, whereas the Ta promotes better adhesion andcrystallographic orientation for the overlying copper seed layer. TheTaN_(x) film may be deposited using a tantalum containing precursor(e.g., TaCl₅, PEMAT, PDEAT, TBTDET) as the first reactant 100 (precursorA) and a mixture of atomic hydrogen and atomic nitrogen (i.e. flowing amixture of H₂ and N₂ into the plasma source 172) as the second reactantto produce a TaN_(x) film. Simultaneous ion exposure is used to drivethe deposition reaction. Next a Ta film may be deposited in a similarfashion by using atomic hydrogen (as opposed to a mixture of atomichydrogen and nitrogen) as the second reactant. An example of a tailoredfilm stack of differing materials can be the subsequent deposition of acopper layer over the TaN_(x)/Ta bi-layer via the use of a coppercontaining organometallic (e.g., Cu(TMVS)(hfac) or(Trimethylvinylsilyl)hexafluoroacetylacetonato Copper I, also known bythe trade name CupraSelect®, available from Schumacher, a unit of AirProducts and Chemicals, Inc., 1969 Palomar Oaks Way, Carlsbad, Calif.92009) or inorganic precursor (e.g. CuCl) shown as precursor C 120 inFIG. 1. The copper layer can serve as the seed layer for subsequentelectroless or electroplating deposition.

[0046] A variant of the method shown in FIG. 2A is illustrated in FIG.2B where ion exposure is initiated after the second reactant exposure.FIG. 2B depicts a sequence for an improved ALD method incorporatingperiodic exposure of the substrate 181 to ions 177. In this variant ofthe method, ion exposure 280 begins with the evacuation 250 of thesecond precursor 256 (especially when the second precursor or reactantis not subjected to a plasma). Typically, this is the case where thesecond precursor or reactant is not a plasma-generated radical.

[0047] In the previous embodiments of MII-ALD, although the depositiontemperature can be lowered significantly, the first and second reactantsare still sequentially introduced into the main process chamber 180, andhence will still be a slow process. It is of particular interest toeliminate or replace the time-consuming flow-evacuation-flow-evacuationsequential nature of the process.

[0048] In the preferred embodiment of the MII-ALD process, a substrate181 heated (e.g., to a low temperature of less than or equal to 350° C.)or unheated is simultaneously exposed to a first reactant and a secondreactant, and subjected to modulated ion 177 exposure. By modulating 1)the ion flux (i.e. the number of ions hitting the substrate per unitarea per unit time); 2) the energy of the ions striking the substrate;or a combination of (1) and (2), the deposition reaction can beprecisely toggled “on” or “off”. Since the substrate 181 is preferablymaintained at a low substrate temperature, the first and secondreactants do not thermally react with any appreciable rate or do notreact at all when the ion flux or energy is toggled to a “low” state.Instead, the deposition reaction only takes place when either the ionflux or ion energy is toggled to a suitable “high state”. Ion flux orenergy modulation can vary generally from 0.1 Hz to 20 MHz, preferablyfrom 0.01 KHz to 10 KHz. During deposition, the main process chamber 180pressure can be maintained in the range of generally 10² to 10⁻⁷ torr,more preferably from 10¹ to 10⁻⁴ torr, depending on the chemistryinvolved. The desired film thickness is attained via exposure of thesubstrate to the suitable number of modulated ion flux or energy pulsecycles. This MII-ALD scheme results in a “continuous” deposition processthat is significantly faster than conventional sequential ALD since thetwo, slow evacuation steps (up to minutes) are eliminated and replacedby the faster (KHz range or above) ion modulation steps. The modulationcan be either of the ion flux via the plasma power or of the ion energyvia an applied periodic wafer bias.

[0049] The MII-ALD method utilizing ion flux modulation to control thedeposition cycle is illustrated conceptually in FIG. 3A, with the fluxmodulation scheme described more explicitly in FIGS. 4A and 4C. FIG. 3Adepicts the MII-ALD method utilizing ion flux modulation 320 to vary thesubstrate 181 exposure to ions 177. Note that the second reactant 310,e.g., radicals, is synchronized with the ion flux via 320 plasma powermodulation, causing a periodic exposure of the substrate to ions andradicals. Varying the power 160 delivered to the plasma 172 can vary theion flux from little or none to maximum ion production. Plasma powermodulation can take the form of variations in frequency (periodicity),magnitude, and duty-cycle. Increasing plasma power 160 leads toincreasing plasma 172, and hence, increased ion 177 density. Since thedeposition process is ion-induced, having little or no ion bombardmentwill essentially stop the deposition process, whereas increased ionbombardment will cause deposition to occur. A constant wafer bias 185(DC in FIG. 4C or RF in FIG. 4A) is applied to define the ion energy ofthe modulated ion flux in this embodiment and is chosen to besufficiently high so that ion-induced surface reactions can occur. Notethat in this embodiment since the plasma (either RF or preferablymicrowave) power 160 is used to generate both ions 177 and radicals 176,the second reactant (e.g., radicals) flux 310 is synchronized with theion flux 320 pulses. The radical feed gas 110 (H₂ for example) flow,however, does not change. Instead, the radical flux 310 (e.g., fractionof H₂ which is converted to atomic H) is modulated.

[0050] Alternatively, subjecting the substrate 181 to a non-constantwafer voltage bias 185 can vary the incoming ion energy at a fixedplasma power 160 (i.e., ion flux). This preferred embodiment of MII-ALDis illustrated conceptually in FIG. 3B, and more explicitly in FIGS. 4Band 4D. FIG. 3B shows the MII-ALD method utilizing ion energy modulation350 to vary the substrate 181 exposure to ions 177 by varying thesubstrate bias 185. The applied bias 185 can take the form of variationsin frequency (periodicity), magnitude, and duty-cycle. A DC as shown inFIG. 4D or RF (e.g., 400 kHz, 2 MHz, 13.56 MHz, etc.) as shown in FIG.4B power supply can be used. When the wafer potential is “low” (e.g.,near or at zero with respect to ground), the incoming ions 177 do nothave enough energy to induce surface deposition reactions. When thewafer 181 potential is “high” (e.g., at a significant negative potentialrelative to ground), the incoming ions 177 will have the necessaryenergy to induce surface deposition reactions via collision cascades. Insuch a fashion, the deposition can be turned “on” or “off” by modulatingthe wafer bias voltage 185, and hence the impinging ion 177 energy.Typical wafer voltages can range from generally −20 V to −1000 V, butpreferably in the −25 V to −500 V range, and more preferably in the −50V to −350 V range during deposition. The bias voltage 185 is coupled tothe wafer via the pedestal 182. Preferably, the substrate pedestal 182is an electrostatic chuck (ESC) to provide efficient coupling of biasvoltage to the substrate. The ESC is situated in the main processingchamber 180 and can be cooled via a fluid coolant (preferably a liquidcoolant) and/or heated (e.g., resistively) to manipulate the substratetemperature.

[0051] As illustrated in FIG. 5 for the case of an applied DC bias, thepreferred electrostatic chuck is a “coulombic” ESC 500 (bulk resistivitygenerally greater than 10¹³ ohm-cm) rather than one whose bulk materialeffects are dominated by the Johnson-Rahbek (JR) effect (bulkresistivity between 10⁸ and 10¹² ohm-cm). Typically, the substratepotential is a complex function of the voltage of the electrostatic“chucking” electrodes if these voltages are established relative to areference potential, but is simplified in the case of “coulombic”(non-JR) ESC. However, if the power supply 510 that powers the ESC 500is truly floating, i.e., the entire system has a high impedance to thechamber 180 potential (usually ground) including the means of supplyingpower, then the substrate potential can be arbitrary. In particular, ifthe ESC power supply 510 is also center-tapped 518, then the waferpotential can be established by connecting the center tap 518 to theoutput of a power amplifier 520. This power amplifier can be controlledby a computer or a waveform generator 530 to periodically drop thesubstrate potential to a negative value for a certain period of time. Itis desired to have independent control of the magnitude, frequency(periodicity), and duty cycle of this substrate bias pulse train. Suchan ESC system is depicted in FIG. 5, which shows an ESC system suitablefor modulating the ion energy in the MII-ALD process: a) in topologicalform; and, b) as an equivalent electrical circuit.

[0052] The deposition rate is affected by the choice of the criticalbias pulse train variables: the magnitude, frequency (periodicity), andduty cycle. Preferably, when the bias frequency is high (e.g., 100 Hz-10KHz) with a short duty cycle (e.g., less than 30%), reducing the net,time-averaged current (which can cause substrate potential drift,de-chucking problems, or charge-induced device damage) while providing acharge relaxation period wherein the ion charges accumulated during ionexposure can redistribute and neutralize.

[0053] Once the deposition rate is calibrated for a particular recipe(Angstroms/cycle), the ability to accurately determine the filmthickness by counting cycles is a further benefit of this modulationscheme. The higher the frequency, the finer the resolution of thiscritical deposition process performance metric.

[0054] Alternatively, the substrate potential can be modulated byimparting an induced DC bias to the substrate by applying RF power tothe pedestal. Preferably, the RF power is coupled into the ESCelectrodes. FIGS. 4A-F illustrate the preferred methods of modulatingthe MII-ALD process. In FIG. 4A, an RF bias power B₂ is applied to thesubstrate pedestal 182 imparting an induced DC bias V₂ to the substratewhile the plasma (either microwave or RF) power 400 is variedperiodically between a high P₁ and a low P₂ power state. In FIG. 4B,plasma (either microwave or RF) power 410 is constant P₁ while an RFbias power, applied to the substrate pedestal 182, is varied between alow B₁ and a high B₂ bias state (V₁ andV₂ are the DC offset or biasvoltages resulting from the applied RF bias power). In FIG. 4C, anegative DC bias 425 is applied to the substrate pedestal 182 while theplasma (either microwave or RF) power 420 is varied periodically betweena high P₁ and a low power P₂ state. In FIG. 4D, plasma (either microwaveor RF) power is constant 430 while a DC bias 435 applied to thesubstrate pedestal 182 is varied between a zero V₁ and a negativevoltage state V₂. In FIG. 4E, a mechanical shutter periodically occludesthe ion source. All the while, the plasma power 440 (either microwave orRF) and substrate voltage 445 are held constant. In FIG. 4F, a sourcearea that is smaller than the substrate 181 is preferably used. In thiscase, plasma (either microwave or RF) power 450 is constant, a negativeDC substrate bias 455 is constant, and the source and substrate 181 aremoved relative to each other 457, exposing only a portion of thesubstrate 181 at a time. The methods proposed in FIG. 4B and FIG. 4D,whereby the substrate bias is modulated at a constant plasma power 410,430 and hence ion flux, are most preferred.

[0055] MII-ALD can be used to deposit dielectric, semiconducting, ormetal films, among others, used in the semiconductor, data storage, flatpanel display, and allied as well as other industries. In particular,the method and apparatus is suitable for the deposition of barrierlayers, adhesion layers, seed layers, low dielectric constant (low-k)films, and high dielectric constant (high-k) films.

[0056] This process utilizes independent control over the threeconstituents of plasma—ions, atoms, and precursors. Decoupling theseconstituents offer improved control over the deposition process.

[0057] An added benefit of using MII-ALD is that with proper choice ofthe second reactant, selective ion-enhanced etching and removal ofunwanted impurities can be performed. As an example, for manychemistries, the preferred second reactant is monatomic hydrogen (H)176. Simultaneous energetic ion and reactive atomic H bombardment willcause selective removal of unwanted impurities (e.g., containing carbon,oxygen, fluorine, or chlorine) commonly associated with organometallicprecursors (e.g., TBTDET, PEMAT, PDEAT, TDMAT, TDEAT), and proceed withremoval rates superior to either chemical reaction (e.g., atomic H only)or physical sputtering (e.g., Ar ion only) alone. Impurities lead tohigh film resistivities, low film density, poor adhesion, and otherdeleterious film effects. Alternatively, in addition to atomic hydrogen,other reactive groups such as nitrogen atoms (N), oxygen atoms (O), OHmolecules, or NH molecules, or a combination thereof may be employed.

[0058] From the description of the preferred embodiments of the processand apparatus set forth above, it is apparent to one of ordinary skillin the art that variations and additions to the embodiments can be madewithout departing from the principles of the present invention. As anexample, chlorine, bromine, fluorine, oxygen, nitrogen, hydrogen, otherreactants and/or radicals containing the aforementioned elements or acombination thereof, in conjunction with energetic ion bombardment, canbe used to effect etching or material removal as opposed to deposition.This is of particular importance in the cleaning of native oxides ofcopper, aluminum, silicon, and other common conductor and semiconductormaterials used in IC manufacturing. Either the deposition or etching canbe accomplished globally (as illustrated in the preceding embodiments)or may be chosen to be local to a controlled area (i.e., site-specificusing a small, ion beam point or broad-beam source scanned or otherwisestepped across the substrate, exposing only a fraction of the substratearea at any given time).

What is claimed is:
 1. A sequential method for depositing a thin filmonto a substrate in a chamber comprising: introducing a first reactantgas into said chamber; adsorption of at least one monolayer of saidfirst reactant gas onto said substrate; removal of excess said firstreactant gas from said chamber introduction of at least one iongenerating feed gas into said chamber; introduction of at least oneradical generating feed gas into said chamber; generating a plasma fromsaid ion generating feed gas and said radical generating feed gas toform ions and radicals; exposing said substrate to said ions and saidradicals; modulating said ions; and reacting said adsorbed monolayer ofsaid first reactant gas with said ions and said radicals to deposit saidthin film.
 2. The method of claim 1, wherein said deposited thin film isat most one monolayer.
 3. The method of claim 1, wherein said method isrepeated until the film achieves a desired thickness.
 4. The method ofclaim 1, wherein a chamber ambient pressure is subatmospheric.
 5. Themethod of claim 1, wherein the removal of said first reactant isachieved through evacuation.
 6. The method of claim 1, wherein saidfirst reactant gas is selected from the group consisting of Tacontaining precursors, W containing precursors, Ti containingprecursors, Mo containing precursors, Hf containing precursors, and Cucontaining precursors.
 7. The method of claim 1, wherein said firstreactant gas is a metal halide.
 8. The method of claim 7, wherein saidmetal halide is selected from the group consisting of TaCl₅, TaBr₅, WF₆,TiCl₄, and CuCl.
 9. The method of claim 1, wherein said first reactantgas is an organometallic.
 10. The method of claim 9, wherein saidorganometallic is selected from the group consisting ofpentakis(diethylamido)tantalum (PDEAT),pentakis(ethylmethylamido)tantalum (PEMAT), t-butyliminotris(diethylamino) tantalum (TBTDET), W(CO)₆,tetrakis(dimethylamido)titanium (TDMAT), tetrakis(diethylamido)titanium(TDEAT), and (Trimethylvinylsilyl)hexafluoroacetylacetonato Copper I(Cu(TMVS)(hfac)).
 11. The method of claim 1, wherein said radicalgenerating feed gas is selected from the group consisting of H₂, O₂, N₂,NH₃, and H₂O vapor.
 12. The method of claim 1, wherein said generatedradicals are selected from a group consisting of hydrogen atoms,nitrogen atoms, oxygen atoms, OH molecules, and NH molecules.
 13. Themethod of claim 1, wherein said ion generating feed gas is selected froma group consisting of Argon, Krypton, Neon, and Xenon.
 14. The method ofclaim 1, wherein said generated ions are selected from a groupconsisting of Ar⁺, Kr⁺, Ne⁺, and Xe⁺.
 15. The method of claim 1, furthercomprising exposing said substrate to at least one additional reactantgas.
 16. The method of claim 1, wherein said substrate is simultaneouslyexposed to said ions and said radicals.
 17. The method of claim 1,wherein said substrate is exposed to said ions after exposure to saidradicals.
 18. The method of claim 1, further comprising electricallybiasing said substrate to a negative potential relative to ground. 19.The method of claim 18, wherein application of said bias occurs duringion exposure.
 20. The method of claim 18, wherein application of saidbias occurs during radical exposure.
 21. The method of claim 18, whereinapplication of said bias occurs during simultaneous ion and radicalexposure.
 22. The method of claim 18, further comprising coupling saidbias to said substrate via a substrate pedestal on which said substraterests.
 23. The method of claim 22, wherein said pedestal is anelectrostatic chuck (ESC) to provide coupling of said bias voltage tosaid substrate.
 24. The method of claim 18, wherein said electrical biasis produced by a direct current power supply.
 25. The method of claim18, wherein said electrical bias is induced by a radio frequency powersupply.
 26. The method of claim 25, wherein said radio frequency isselected from the group consisting of 400 kHz, 2 MHz, and 13.56 MHz. 27.The method of claim 18, wherein said negative potential is between about−20 V to −1000 V relative to ground.
 28. The method of claim 27, whereinsaid negative potential is between about −25 V to −500 V relative toground.
 29. The method of claim 28, wherein said negative potential isbetween about −50 V to −350 V relative to ground.
 30. The method ofclaim 1, further comprising said ions and said radicals removingunwanted impurities from said substrate prior to said adsorption of saidmonolayer of the first reactant.
 31. The method of claim 1, furthercomprising said ions and said radicals removing unwanted impurities fromsaid monolayer during said film deposition reaction.
 32. The method ofclaim 30, wherein said unwanted impurities are selected from the groupconsisting of carbon-, oxygen-, fluorine-, and chlorine-containingimpurities.
 33. The method of claim 31, wherein said unwanted impuritiesare selected from the group consisting of carbon-, oxygen-, fluorine-,and chlorine-containing impurities.
 34. The method of claim 30, whereinsaid monolayer is an organometallic.
 35. The method of claim 30, whereinsaid monolayer is a metal halide.
 36. The method of claim 31, whereinsaid monolayer is an organometallic.
 37. The method of claim 31, whereinsaid monolayer is a metal halide.
 38. The method of claim 30, whereinsaid radicals are selected from the group consisting of hydrogen atoms,nitrogen atoms, OH molecules, and NH molecules.
 39. The method of claim31, wherein said radicals are selected from the group consisting ofhydrogen atoms, nitrogen atoms, OH molecules, and NH molecules.
 40. Themethod of claim 30, wherein said ions are selected from a groupconsisting of Ar⁺, Kr⁺, Ne⁺, and Xe⁺.
 41. The method of claim 31,wherein said ions are selected from a group consisting of Ar⁺, Kr⁺, Ne⁺,and Xe⁺.
 42. The method of claim 1, wherein said ion modulation ismodulated in a way selected from the group consisting of modulating anion flux and modulating an ion energy.
 43. The method of claim 42,wherein modulation in said ion flux is modulated in a way selected fromthe group consisting of modulating a flow of said ion generating feedgas, modulating a power of said plasma, modulating said exposure to saidions, and modulating the relative movement between said plasma and saidsubstrate.
 44. The method of claim 43, wherein said exposure ismodulated by mechanically occluding said ions.
 45. The method of claim42, wherein said ion energy modulation occurs by modulating a magnitudeof a negative potential bias on said substrate.
 46. The method of claim45, wherein said modulation of negative potential magnitude is effectedin a way selected from the group consisting of changing a direct currentbias potential on said substrate and changing a radio frequency powerand inducing a change in said substrate bias potential.
 47. The methodof claim 1, further comprising maintaining said substrate at atemperature of between about 25° C. to 350° C.
 48. The method of claim47, wherein said temperature is maintained between about 20° C. to 25°C.
 49. The method of claim 48, wherein said temperature is maintainedbetween about 100° C. to 200° C.
 50. The method of claim 1, wherein thepressure of said chamber is maintained in a range of approximately 10²to 10⁻⁷ torr during processing.
 51. The method of claim 50, wherein thepressure of said chamber is maintained in a range of approximately 1 to10⁻⁴ torr during processing.
 52. The method of claim 1, wherein saidadsorption of said monolayer of said first reactant gas on saidsubstrate occurs via chemisorption.
 53. The method of claim 1, whereinsaid method is followed by a sequential method for depositing a secondthin film onto said substrate comprising: introducing a second reactantgas into said chamber; adsorption of at least one monolayer of saidsecond reactant gas onto said substrate; evacuation of excess saidsecond reactant gas from said chamber introduction of at least one iongenerating feed gas into said chamber; introduction of at least oneradical generating feed gas into said chamber; generating a plasma fromsaid ion generating feed gas and said radical generating feed gas toform ions and radicals; exposing said substrate to said ions and saidradicals; modulating said ions; and reacting said adsorbed monolayer ofsaid second reactant gas with said ions and said radicals to depositsaid second thin film.